It is known that cases which have openings connected to the engine, downstream of the filter in comparison to the air flow, will introduce strong resistances and turbulences that cause the drawback of reduced air flow to the engine.
It is known to provide cases for filters with an inner link between the inlet opening and the side wall sized to reduce the air resistance.
A drawback of such filtering devices consists in that the link allows the passage of a possible extraneous object, for instance nuts or screw forgotten or fallen in the case of the filter, in the inlet collectors of the engine with serious damage risks. The risk of an extraneous object being present is particularly relevant in a racing filter device as these are continuously being opened for inspections, cleaning, substitution also during the hurried work being performed on different parts of the engine at the same time.
Further drawbacks of the known filters are that they increase the weight and they reduce the inside volume for the air.
U.S. Pat. No. 4,695,299 discloses a cyclone having at its upper outlet side a filter. The filter comprises a tubular housing having an inlet at its lower end and an outlet at its opposite upper end. A cylindrical filter element is installed in connection with the inlet opening and a tubular body forming the outlet opening protrudes towards inside said tubular casing.